Driving apparatus, lens driving apparatus and image pickup apparatus

ABSTRACT

A driving apparatus comprises an actuator, the actuator comprising an electromechanical conversion element and a driving shaft attached to the electromechanical conversion element, wherein the driving apparatus expands and contracts the electromechanical conversion element by applying a driving signal to the electromechanical conversion element and reciprocally moves the driving shaft in accordance with expansion and contraction movement of the electromechanical conversion element so as to move a driven member frictionally engaged with the driving shaft, and wherein the driving signal is a pulse signal, and a time period corresponding to a half wavelength of a damping vibration displacement of a lowest resonance frequency in the actuator is set as a shorter output time among a high output time period and a low output time period of the driving signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a driving apparatus using anelectromechanical conversion element such as a piezoelectric element, alens driving apparatus and an image pickup apparatus using the same.

2. Description of the Related Art

In the related art, as a driving apparatus using an electromechanicalconversion element such as a piezoelectric element, there is known adriving apparatus which includes an electromechanical conversion elementwhich expands and contracts in accordance with a voltage appliedthereto, a drive friction member fixed to one end in the expansion andcontraction direction of the electromechanical conversion element, anengaging member frictionally engaging with the drive friction member,and a driving circuit which applies the voltage to the electromechanicalconversion element (for example, Japanese Patent No. 3646154).

The driving apparatus of Japanese Patent No. 3646154 intends to performa low speed driving stably by inputting a predetermined driving signalto the electromechanical conversion element. In such a kind of drivingapparatus, it is desired to improve the driving efficiency and move adriven member at a high speed as high as possible.

SUMMARY OF THE INVENTION

Accordingly, the invention has been made in order to solve the aforesaidproblem of the related art and an object of the invention is to providea driving apparatus which can increase the moving speed of a drivenmember, a lens driving apparatus and an image pickup apparatus using thesame.

According to an aspect of the invention, there is provided a drivingapparatus comprising an actuator, the actuator comprising anelectromechanical conversion element and a driving shaft attached to theelectromechanical conversion element, wherein the driving apparatusexpands and contracts the electromechanical conversion element byapplying a driving signal to the electromechanical conversion elementand reciprocally moves the driving shaft in accordance with expansionand contraction movement of the electromechanical conversion element soas to move a driven member frictionally engaged with the driving shaft,and wherein the driving signal is a pulse signal, and a time periodcorresponding to a half wavelength of a damping vibration displacementof a lowest resonance frequency in the actuator is set as a shorteroutput time among a high output time period and a low output time periodof the driving signal.

According to the aspect of the invention, pulse signals are used as thedriving signal for the electromechanical conversion element, and thetime period corresponding to the half wavelength of the dampingvibration displacement of the lowest resonance frequency in the actuatoris set as the shorter output time among the high output time periods andthe low output time periods of the drive signal. Thus, the moving speedof the driven member can be made higher.

In the driving apparatus according to the aspect of the invention, in acase where an off output is set in the driving signal, it is preferredthat the time period corresponding to the half wavelength of the dampingvibration displacement is set as the shorter output time among the highoutput time period and the low output time period, while time period ofthe off output appearing after high output or low output is contained inthe high output time period or the low output time period.

Further, in the driving apparatus according to the aspect of theinvention, it is preferred that the actuator is supported from sidedirection in expansion and contraction directions of theelectromechanical conversion element and attached, and each of both endsof the actuator serves as a free end movable in the expansion andcontraction directions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional diagram showing a driving apparatus according tothe embodiment of the invention;

FIG. 2 is a sectional diagram showing a driven member cut along a lineII-II in FIG. 1;

FIG. 3 is a circuit diagram showing a driving circuit in the drivingapparatus in FIG. 1;

FIGS. 4A and 4B are diagrams showing waveforms of a driving signalinputted into the piezoelectric element of the driving apparatus in FIG.1;

FIG. 5 is a diagram showing the relation between the driving frequencyand the impedance of the actuator of the driving apparatus in FIG. 1;

FIG. 6 is a diagram showing the damping vibration changingcharacteristics in the resonance frequency of the actuator of thedriving apparatus in FIG. 1;

FIG. 7 is a diagram showing the relation between a pulse time period t1and the moving speed in the driving apparatus in FIG. 1;

FIGS. 8A and 8B are diagrams showing a modified example of the drivingsignal in the driving apparatus in FIG. 1; and

FIGS. 9A and 9B are diagrams showing another modified example of thedriving signal in the driving apparatus in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of the invention will be explained withreference to accompanying drawings. In the explanation of the drawings,same elements are referred to by the common symbols, with duplicatedexplanation thereof being omitted.

FIG. 1 is a sectional diagram of a driving apparatus according to theembodiment. As shown in FIG. 1, the driving apparatus according to theembodiment is constituted to include an actuator 10 configured byattaching a driving shaft 2 to a piezoelectric element 1, toreciprocally move the driving shaft 2 in accordance with the expansionand contraction of the piezoelectric element 1, and to move a drivenmember 3 frictionally engaging with the driving shaft 2 along thedriving shaft 2.

The piezoelectric element 1 is an electromechanical conversion elementwhich can expand and contract in a predetermined direction in accordancewith a driving signal applied thereto. The piezoelectric element 1 iscoupled to a control portion 81 and expands and contracts when receivingan electric signal from the control portion 81. For example, thepiezoelectric element 1 is provided with two input terminals 11 a, 11 b.The piezoelectric element 1 repeatedly expands and contracts when thevoltages applied to the input terminals 11 a, 11 b are repeatedlyincreased and reduced.

As the electromechanical conversion element, an element other than thepiezoelectric element 1 may be employed so long as the element expandsand contracts in accordance with the driving signal.

The driving shaft 2 is attached to the piezoelectric element 1 in amanner that the longitudinal direction thereof coincides with theexpansion and contraction directions of the piezoelectric element 1. Forexample, the one end of the driving shaft 2 is abutted against thepiezoelectric element 1 and adhered thereto by using adhesive 21. Thedriving shaft 2 is a long member of a cylindrical shape, for example.The driving shaft 2 is supported so as to be movable in the longitudinaldirection by a partition portion 4 b and a partition portion 4 c eachextending inside from a fixed frame 4. Each of the partition portion 4 band the partition portion 4 c is a member for partitioning the movablearea of the driven member 3 and also acts as a support member for thedriving shaft 2. The fixed frame 4 acts as a casing for housing thepiezoelectric element 1, the driving shaft 2 and the driven member etc.therein and assembling them.

Light-weighted and high-rigidity material is suitable for the materialof the driving shaft 2 and beryllium is ideal material satisfying suchconditions. However, this material is rare metal and so has drawbacksthat the price is high and the forming property is bad. Thus, in thisembodiment, graphite compound which is formed by rigidly conjugatinggraphite crystal, for example, carbon graphite is employed. (In thiscase, the graphite compound means compound of graphite, which ishexagonal plate-shaped crystallization of carbon, and material otherthan graphite, and the carbon graphite means material formed by graphiteand amorphous carbon. Further, graphite is also called as block lead.)The carbon graphite as the graphite compound has property similar toberyllium (the specific gravity of beryllium is about 1.85 and that ofthe carbon graphite is about 1.8) but also has properties that, unlikeberyllium, the cost is relatively low and the forming property is good.The shape of the driving shaft 2 is not limited to cylindrical but maybe rectangular columnar.

Each of the partition portions 4 b and 4 c is provided with a throughhole 4 a for passing the driving shaft 2 therethrough. The partitionportion 4 b supports a portion near the attachment portion of thepiezoelectric element 1 of the driving shaft 2, that is, the base endportion of the driving shaft 2. The partition portion 4 c supports thetip end portion of the driving shaft 2. Since the driving shaft 2 isattached to the piezoelectric element 1, the piezoelectric elementreciprocally moves along its longitudinal direction in accordance withthe repetitive expansion and contraction operations of the piezoelectricelement 1.

FIG. 1 shows the case where the driving shaft 2 is supported at the twoportions, that is, the tip end side and the base end side thereof by thepartition portions 4 b, 4 c. However, there is a case where the drivingshaft 2 is supported at one of the tip end side and the base end sidethereof. For example, when the diameter of the through hole 4 a of thepartition portion 4 b is formed to be larger than the outer diameter ofthe driving shaft 2, the driving shaft 2 is supported only at its tipend portion by the partition portion 4 c. In contrast, when the diameterof the through hole 4 a of the partition portion 4 c is formed to belarger than the outer diameter of the driving shaft 2, the driving shaft2 is supported only at its base end portion by the partition portion 4b.

Further, although FIG. 1 shows the case where the partition portions 4b, 4 c for supporting the driving shaft 2 is integrated with the fixedframe 4, the partition portions 4 b, 4 c may be provided separately fromthe fixed frame 4 and then attached thereto. Even if the partitionportions are provided separately from the fixed frame, the function andeffects similar to those in the case where the partition portions areprovided integrally with the fixed frame can be obtained.

The driven member 3 is attached to the driving shaft 2 so as to bemovable. The driven member 3 is frictionally engaged with the drivingshaft 2 and is movable along the longitudinal direction of the drivingshaft 2. For example, the driven member 3 is attached to the drivingshaft in a manner that the driven member is made in contact with thedriving shaft 2 by a leaf spring 7 so as to engage therewith at apredetermined friction coefficient, and a constant friction force iscaused when the driven member moves since the driven member is pressedagainst the driving shaft 2 by a constant pressing force. When thedriving shaft 2 moves so as to exceed the friction force, the drivenmember 3 maintains its position due to the inertia and so the drivingshaft 2 moves relatively with respect to the driven member 3.

The piezoelectric element 1 is attached to the fixed frame 4 by means ofa support member 5. The support member 5 serves to attach thepiezoelectric element to the fixed frame in a manner that the supportmember supports the piezoelectric element 1 from the side direction withrespect to the expansion and contraction direction thereof. The supportmember is disposed between the piezoelectric element 1 and the fixedframe 4. In this case, the support member 5 preferably supports thepiezoelectric element 1 from the direction orthogonal to the expansionand contraction direction thereof. The support member 5 serves as anattachment member for attaching the piezoelectric element in a manner ofsupporting the piezoelectric element 1 from the side direction thereof.

In this manner, the actuator 10 is supported by the support member 5from the side direction with respect to the expansion and contractiondirection of the piezoelectric element 1, and so the both ends of theactuator 10 serve as free ends movable in the expansion and contractiondirection of the piezoelectric element 1. Thus, when the actuator 10 isdriven, the vibration due to the expansion and contraction of thepiezoelectric element 1 is hardly transmitted to the fixed frame 4 side.Therefore, it is effective to set the driving signal of the actuator 10in relation to the resonance frequency of the actuator 10.

The support member 5 is formed by elastic material having predeterminedelastic characteristics or more, for example, by silicon resin. Thesupport member 5 is configured so as to have the insertion hole 5 a forinserting the piezoelectric element 1 there into and is assembled intothe fixed frame 4 in a state that the piezoelectric element 1 isinserted into the insertion hole 5 a. The support member 5 is fixed tothe fixed frame 4 by means of adhesive 22. The support member 5 is alsofixed to the piezoelectric element 1 by means of adhesive. Since thesupport member 5 is formed by the elastic material, the support member 5can support the piezoelectric element 1 so as to be movable in theexpansion and contraction thereof. In FIG. 1, although the two supportmember 5 are shown on the both aides of the piezoelectric element 1, thesupport member 5 is shown in the two pieces 5, 5 in its sectional view.

The support member 5 may be fixed to the fixed frame 4 and thepiezoelectric element 1 in a manner that the support member 5 is pressedbetween the fixed frame 4 and the piezoelectric element 1 and then thefixed frame and the piezoelectric element are pressed by the supportmember 5. For example, the support member 5 is formed by the elasticmaterial so as to have a width larger than a space between the fixedframe 4 and the piezoelectric element 1, and the support member ispressed therebetween. Thus, the support member 5 is disposed in aclosely adhered manner between the fixed frame 4 and the piezoelectricelement 1. In this case, the piezoelectric element 1 is pressed from theboth ends thereof orthogonal to the expansion and contraction thereof bythe support member 5, whereby the piezoelectric element 1 is supported.

Although the explanation is made as to the case where the support member5 is formed by the silicon resin, the support member 5 may be formed bya spring member. For example, the spring member may be disposed betweenthe fixed frame 4 and the piezoelectric element 1 so as to support thepiezoelectric element 1 with respect to the fixed frame 4 by the springmember.

A movable lens 90 is attached to the driven member 3 via a lens frame91. The movable lens 90 constitutes the image pickup optical system of acamera and a subject moved by the driving apparatus. The movable lens 90is provided integrally with the driven member 3 so as to move togetherwith the driven member 3. A not-shown fixed lens etc. are disposed onthe optical axis O of the movable lens 90 thereby to constitute theimage pick-up optical system of the camera. Further, an image pickupelement 82 is disposed on the optical axis O. The image pickup element82 is an image-pickup element which converts an image picked-up by theimage pickup optical system into an electrical signal and is formed by aCCD, for example. The image pickup element 82 is coupled to the controlportion 81 and outputs the image signal to the control portion 81.

The weight member 6 is attached to the end portion of the piezoelectricelement 1. The weight member 6 acts to transmit the expansion andcontraction force of the piezoelectric element 1 on the driving shaft 2side and so attaché to the end portion of the piezoelectric element 1 onthe opposite end portion side thereof where the driving shaft 2 isattached.

The weight member 6 constitutes a part of the actuator 10. The weightmember 6 is selected to have a weight lager than that of the drivingshaft 2. The weight member 6 is preferably formed by mixing metallicpowder into an elastically deformable member The weight of the weightmember can be made large by mixing the metal powder, and the unnecessaryresonance of the weight member can be reduced at the time of theoperation of the piezoelectric element 1 by employing the elasticallydeformable member.

The material of the weight member 6 is selected to have a Young'smodulus smaller than those of the piezoelectric element 1 and thedriving shaft 2. The Young's modulus of the weight member 6 ispreferably 1 GPa or less and more preferably 300 Mpa or less. Such theweight member 6 can be formed by mixing the metallic power having alarge specific gravity into elastic material such as robber. Forexample, the weight member can be manufactured by mixing tungsten powderinto urethane rubber or urethane resin. The specific gravity of theweight member 6 is preferably as high as possible in order tominiaturize the apparatus and so set almost in a range from 8 to 12, forexample. The Young's modulus and the specific gravity of the weightmember 6 manufactured by mixing tungsten powder into urethane rubber orurethane resin are almost 60 Mpa and 11.7, respectively. Thus, in thecase of designing the weight member 6 so as to have a volume as small aspossible, such a combination is best where the specific gravity is aslarge as possible and the Young's modulus is small. However, the weightmember is useful so long as the specific gravity thereof is larger thanthat of the driving shaft 2 (1.8 or more) and the Young's modulusthereof is 1 GPa or less. That is, the weight member 6 is suitable whena numerical value obtained by dividing the specific gravity by theYoung's modulus (specific gravity/Young's modulus) is 1.8×10⁻⁹ or more.The adhesive for fixing the weight member 6 with the piezoelectricelement 1 is preferably elastic adhesive.

Further, the weight member 6 is provided in a state of not beingsupported by or fixed to the fixed frame 4. That is, the weight member 6is provided in a state that the weight member is attached to the freeend of the piezoelectric element 1 and not directly supported by orfixed to the fixed frame 4, and further is not directly supported by orfixed so as to be restricted in its movement with respect the fixedframe 4 via adhesive or resin material.

The actuator 10 may be configured without providing the weight member 6.That is, the actuator 10 maybe configured without attaching the weightmember 6 to the end potion of the piezoelectric element 1 and hence maybe configured by attaching the driving shaft 2 to the piezoelectricelement 1.

The driving apparatus is provided with a detector 83 for detecting themoving position of the driven member 3. For example, an optical detectorhaving a photo reflector or a photo interrupter etc. is employed as thedetector 83. To be concrete, in the case of using the detector 83 havinga reflector 83 a and a detection portion 83 b, the reflector 83 a isattached to the lens frame 91 integrally formed with the driven member3, whereby detection light is emitted from the detection portion 83 b tothe reflector 83 a side and the detection portion 83 b detectsreflection light reflected from the reflector 83 a side thereby todetect the moving position of the driven member 3 and the movable lens90.

The detector 83 is coupled to the control portion 81. An output signalfrom the detector 83 is inputted into the control portion 81. Thecontrol portion 81 serves to control the driving apparatus entirely andis configured by a CPU, a ROM, a RAM, an input signal circuit and anoutput signal circuit etc., for example. The control portion 81 includesa driving circuit for operating the piezoelectric element 1 and suppliesan electric signal for driving to the piezoelectric element 1.

FIG. 2 is a sectional diagram showing a frictionally engaging portion ofthe driven member 3 cut along a line II-II in FIG. 1.

As shown in FIG. 2, the driven member 3 is attached to the driving shaft2 since the driving shaft 2 is pressed by the leaf spring 7. Forexample, a groove 3 a of a V-shape for positioning the driving shaft 2is formed in the driven member 3. A sliding plate 3 b of a V-shape inits section is disposed in the groove 3 a, whereby the driving shaft 2is pressed against the driven member 3 via the sliding plate 3 b.

A sliding plate 3 c of a V-shape in its section is disposed between theleaf spring 7 and the driven member 3. The leaf spring 7 presses thedriven member 3 via the sliding plate 3 c. The sliding plates 3 b, 3 care disposed in a manner that the concave portion sides thereof areopposed to each other so as to sandwich the driving shaft 2therebetween. Since the driving shaft 2 is housed within the V-shapedgroove 3 a, the driven member 3 can be attached to the driving shaft 2stably.

A leaf spring member of an L-shape in its section, for example, is usedas the leaf spring 7. When one side of the leaf spring 7 is engaged withthe driven member 3 and the other end thereof is disposed at a positionopposing to the groove 3 a, the driving shaft 2 housed within the groove3 a can be sandwiched between the driven member 3 and the other end ofthe leaf spring.

In this manner, since the driven member 3 is attached in a manner ofbeing pressed by a constant force against the driving shaft 2 side bythe leaf spring 7, the driven member 3 is frictionally engaged with thedriving shaft 2. That is, the driven member 3 is attached in a mannerthat the driven member 3 is pressed against the driving shaft 2 with theconstant pressing force and so a constant friction force is caused whenthe driven member moves.

Further, since the driving shaft 2 is sandwiched between the slidingplates 3 b, 3 c each having the V-shape in its section, the drivenmember 3 is made in line-contact with the driving shaft 2 at pluralpoints thereof, whereby the driven member can be frictionally engagedwith the driving shaft 2 stably. Furthermore, since the driven member 3is made in line-contact with the driving shaft 2 at the plural pointsthereof, the driven member 3 is substantially placed in a state of beingengaged with the driving shaft 2 in a plane-contact state, whereby astable frictional engagement can be realized.

FIG. 3 is a circuit diagram showing a driving circuit for operating thepiezoelectric element 1.

As shown in FIG. 3, the driving circuit 85 is disposed within thecontrol portion 1. The driving circuit 85 acts as a driving circuit forthe piezoelectric element 1 and outputs the electric signal for drivingto the piezoelectric element 1. The driving circuit 85 inputs a controlsignal from the control signal generation portion (not shown) of thecontrol portion 81, then voltage-amplifies or current-amplifies thecontrol signal and outputs the amplified signal to the piezoelectricelement 1 as the driving electric signal. As the driving circuit 85,there is employed one which input stage is configured by logic circuitsU1 to U3 and output stage is configured by field effect transistors(FETs) Q1, Q2, for example. Each of the transistors Q1, Q2 is configuredso as to be able to output a Hi output (high-voltage output), a Looutput (low-voltage output) and an OFF output (off output or openoutput) as an output signal.

The driving circuit thus configured is an example of the circuits foroperating the piezoelectric element 1 and the piezoelectric element 1may be operated by using a circuit configured in a different manner.

FIGS. 4A and 4B show an example of the driving signal outputted from thedriving circuit 85.

FIG. 4A shows the driving signal inputted into the piezoelectric element1 in the case of moving the driven member 3 in a direction (rightdirection in FIG. 1) approaching the piezoelectric element 1, and FIG.4B shows the driving signal inputted into the piezoelectric element 1 inthe case of moving the driven member 3 in a direction (left direction inFIG. 1) separating from the piezoelectric element 1.

In the driving signals shown in FIGS. 4A and 4B, an Aout signal isapplied to the one input terminal 11 a of the piezoelectric element 1and a Bout signal is applied to the other input terminal 11 b of thepiezoelectric element 1. Thus, the difference between the signals Aoutand Bout is applied to the piezoelectric element 1 as the input voltage.

Although the driving signal of FIGS. 4A and 4B has a rectangularwaveform, the waveform actually inputted into the piezoelectric element1 is a triangular waveform due to the capacitor component of thepiezoelectric element 1. Thus, when the duty ratio between the high andlow levels of the driving signal is not 50%, the expansion speed and thecontraction speed of the piezoelectric element 1 can be differentiatedby the driving signal of the rectangular shape inputted to thepiezoelectric element thereby to move the driven member 3.

Each of the driving signals shown in FIGS. 4A and 4B is a pulse signal,and as an output time period of shorter one between the high (Hi) outputtime period and the low (Lo) output time period of the pulse signal, atime period corresponding to a half wavelength of the damping vibrationdisplacement of the lowest resonance frequency in the actuator 10 isset.

For example, in the driving signals shown in FIGS. 4A and 4B, as theshortest output time among the high (Hi) output time periods and the low(Lo) output time periods of the Aout and Bout signals, a time periodcorresponding to a half wavelength of the damping vibration displacementof the lowest resonance frequency in the actuator 10 is set. In thiscase, the “time period corresponding to a half wavelength of the dampingvibration displacement of the lowest resonance frequency” contains notonly the time period corresponding to a half wavelength but also a timeperiod corresponding to almost a half wavelength. For example, a timeperiod deviated by a range from 20% to −20% from the time periodcorresponding to the half wavelength may be set as the shortest outputtime among the high output time periods and the low output time periodsof the drive signal. Further, more preferably, a time period deviated bya range from 10% to −10% from the time period corresponding to the halfwavelength may be set as the shortest output time among the high outputtime periods and the low output time periods of the drive signal.

FIG. 5 shows the relation between the driving frequency and theimpedance of the actuator 10.

The driving frequency/impedance characteristics shown in FIG. 5 isobtained by measuring the impedance of the piezoelectric element 1 inthe case where the piezoelectric element 1 attached with the drivingshaft 2 and the weight member 6 is used as the actuator 10 and thefrequency of the driving signal inputted to the piezoelectric element 1is changed.

As shown in FIG. 5, a frequency where the impedance drops on the lowestfrequency side, that is, a resonance frequency fr is 330 KHz. That is,the lowest resonance frequency of the actuator 10 is 330 KHz.

The damping vibration displacement x in the resonance frequency fr ofthe actuator 10 is shown by the following expression (1).x=e ^(−k·t)·sin(2π·fr·t)   (1)

In this expression (1), k is a constant and is equal to 2π·fr/2Q, forexample. Q is a predetermined constant. FIG. 6 is a graph showing thedamping vibration displacement x of this expression (1). That is, inFIG. 6, the abscissa represents a time t and the ordinate represents thedamping vibration displacement x. As clear from the graph of FIG. 6, thedamping vibration displacement x changes in a sine wave manner in amanner that the amplitude thereof reduces gradually. A time period ofthe first half wavelength of the damping vibration displacement x is1.5μ second.

Thus, in the driving apparatus according to the embodiment, the timeperiod 1.5μ second of the half wavelength is set as the shortest timeperiod t1 among the high output time periods and the low output timeperiods of the drive signal. When the driving signal is set in thismanner and the driving signal is inputted into the piezoelectric element1, the driven member 3 can be moved in a highest speed state.

FIG. 7 shows the relation between the time period t1 of the drivingsignal and the moving speed of the driven member 3.

The relation shown in FIG. 7 is obtained by measuring the moving speedof the driven member 3 in the case where the time period t1 of thedriving signal inputted into the piezoelectric element 1 of the drivingapparatus is changed. In this measurement, the moving speed is measuredin a manner that the frequency of the driving signal is set to 53 kHzand only the time period t1 is changed. As shown in FIG. 6, the movingspeed becomes faster when the time period t1 is made longer graduallyfrom a short time period, then reaches the maximum speed near the timeperiod of 1.5μ second and becomes slower as the time period t1 is mademore longer.

In this manner, when the time period corresponding to the halfwavelength of the damping vibration displacement in the lowest resonancefrequency of the actuator 10 is set as the shortest output time t1 amongthe high output time periods and the low output time periods of thedrive signal, the driving speed of the driving apparatus can be set tothe highest speed state.

Further, as shown in FIGS. 8A and 8D, there is a case where an offoutput is set in addition to the high output and the low output. Whenthe off output is set in this manner, a through current is preventedfrom flowing through the transistors Q1, Q2 or the driving circuit 85 inthe case of changing the output between the high output and the lowoutput. In this case, the time period (t1 in FIGS. 8A and 8B)corresponding to the half wavelength of the damping vibrationdisplacement is preferably set so as to also contain the off outputperformed after the high output and the low output. When the time periodcorresponding to the half wavelength of the damping vibrationdisplacement is set in this manner, the moving speed of the drivenmember 3 can be set to the highest speed state.

The driving signal may be formed in a manner that the waveform inputtedinto the piezoelectric element 1 exhibits a stepwise shape. For example,as shown in FIGS. 9A and 9B, the driving signal is formed by tworectangular pulse signals having the same frequency in a manner that thephases of these two pulse signals are made different thereby to form thesignals in which the voltage difference therebetween becomes largerstepwise and becomes smaller rapidly or the signals in which the voltagedifference therebetween becomes larger rapidly and becomes smallerstepwise. When such the two kinds of signals are inputted, the expansionspeed and the contraction speed of the piezoelectric element 1 can bemade different thereby to move the driven member 3.

A signal having the frequency exceeding the audio frequency is employedas the driving signal for the driving apparatus according to theembodiment. In FIGS. 4A, 4B, 8A, 8B, 9A and 9B, each of the two signalsAout and Bout is set to have a frequency exceeding the audio frequencyand so set to have a frequency in a range from 30 to 80 Hz, for example,and preferably in a range from 40 to 60 Hz. When the signals each havingsuch the frequency range is used, operation sound in the audio frequencygenerated from the piezoelectric element 1 can be reduced.

Next, the operation of the driving apparatus according to the embodimentwill be explained.

In FIG. 1, when the driving signal is inputted into the piezoelectricelement 1, the piezoelectric element 1 repeatedly expands and contractsin accordance with the driving signal. The driving shaft 2 reciprocallymoves in accordance with the expansion and contraction of thepiezoelectric element. In this case, when the expansion speed andcontraction speed of the piezoelectric element 1 are made different, thespeed of the driving shaft 2 moving In the one direction differs fromthe speed thereof in the opposite direction. Thus, the driven member 3ands the movable lens 90 can be moved in a desired direction.

When the piezoelectric element 1 expands and contracts, a vibration iscaused due to the expansion and contraction thereof. However, since thepiezoelectric element 1 is supported from the side direction withrespect to the expansion and contraction directions by the supportmember 5, the vibration caused by the expansion and contraction of thepiezoelectric element 1 is hardly transmitted to the outside of thepiezoelectric element 1 and the driving shaft 2. Thus, the piezoelectricelement 1 and the driving shaft 2 are suppressed from resonating withthe external members such as the fixed frame 4 and so the influence ofthe resonance can be reduced. Therefore, the driven member 3 and themovable lens 90 can be moved accurately.

As described above, according to the driving apparatus of theembodiment, the pulse signals are used as the driving signal for thepiezoelectric element 1, and the time period corresponding to the halfwavelength of the damping vibration displacement of the lowest resonancefrequency in the actuator 10 is set as the shorter output time among thehigh output time periods and the low output time periods of the drivesignal. Thus, the moving speed of the driven member 3 can be madehigher.

Further, according to the driving apparatus of the embodiment, theactuator 10 is attached so as to be supported from the side directionwith respect to the expansion and contraction directions of thepiezoelectric element 1, and each of the both ends thereof is set as thefree end movable in the expansion and contraction directions. Thus, evenwhen the actuator 10 is driven, the vibration caused by the expansionand contraction operation of the piezoelectric element 1 is hardlytransmitted to the fixed frame 4 side. Thus, it is effective to set thedriving signal of the actuator 10 in relation to the resonance frequencyof the actuator 10 itself. Therefore, when the time period correspondingto the half wavelength of the damping vibration displacement of thelowest resonance frequency in the actuator 10 is set as the shorteroutput time among the high output time periods and the low output timeperiods of the drive signal, the high-speed movement control of thedriven member 3 can be performed surely.

Further, according to the driving apparatus of the embodiment, since thehighest moving speed of the driven member 3 can be further increased,the moving speed of the driven member 3 can be controlled in a widerange from a low speed to a high speed.

Further, in the development and design of the driving apparatus, sincethe setting of the driving signal can be made easily, the design periodcan be shortened.

Furthermore, when the driving apparatus according to the embodiment isused as an actuator for a constituent part in the image pickup opticalsystem of a camera, the size of a driving mechanism can be made smalland so the camera can be miniaturized. Further, when the drivingapparatus according to the embodiment is used as an actuator for aconstituent part in the image pickup optical system of a camera for amobile phone, the size of a driving mechanism can be made small and sothe mobile phone can be miniaturized. Furthermore, the driving apparatusaccording to the embodiment can also be used as an actuator for a webcamera etc.

The aforesaid embodiment shows only an example of the driving apparatusaccording to the invention. The driving apparatus according to theinvention is not limited to the driving apparatus according to theembodiment, and the driving apparatus according to the embodiment may bemodified or may be applied to another device in a scope not departingfrom the gist described in the respective claims.

For example, although the embodiment is explained as to the apparatuswhich is applied to the driving apparatus for driving the movable lens,the invention may be applied to a driving apparatus for driving a deviceother than the movable lens.

Further, although the embodiment is explained as to the case where thepiezoelectric element 1 is attached to the fixed frame 4 via the supportmember 5 thereby to set the end portion of the piezoelectric element 1as the free end, the end portion of the piezoelectric element 1 may bedirectly attached to the fixed frame 4.

According to the invention, the time period corresponding to the halfwavelength of the damping vibration displacement of the lowest resonancefrequency in the actuator is set as the shorter output time among thehigh output time periods and the low output time periods of the drivesignal. Thus, the moving speed of the driven member can be made higher.

The entire disclosure of each and every foreign patent application fromwhich the benefit of foreign priority has been claimed in the presentapplication is incorporated herein by reference, as if fully set forth.

1. A driving apparatus comprising an actuator, the actuator comprisingan electromechanical conversion element and a driving shaft attached tothe electromechanical conversion element, wherein the driving apparatusexpands and contracts the electromechanical conversion element byapplying a driving signal to the electromechanical conversion elementand reciprocally moves the driving shaft in accordance with expansionand contraction movement of the electromechanical conversion element soas to move a driven member frictionally engaged with the driving shaft,and wherein the driving signal is a pulse signal, and a time periodsubstantially equal to a half wavelength of a damping vibrationdisplacement of a lowest resonance frequency in the actuator is set as ashorter output time among a high output time period and a low outputtime period of the driving signal.
 2. A driving apparatus according toclaim 1, wherein in a case where an off output is set in the drivingsignal, the time period corresponding to the half wavelength of thedamping vibration displacement is set as the shorter output time amongthe high output time period and the low output time period, while timeperiod of the off output appearing after high output or low output iscontained in the high output time period or the low output time period.3. A driving apparatus according to claim 1, wherein the actuator issupported from side direction in expansion and contraction directions ofthe electromechanical conversion element, and each of both ends of theactuator serves as a free end movable in the expansion and contractiondirections.
 4. A driving apparatus according to claim 2, wherein theactuator is supported from side direction in expansion and contractiondirections of the electromechanical conversion element and attached, andeach of both ends of the actuator serves as a free end movable in theexpansion and contraction directions.
 5. A lens driving apparatuscomprising: the driving apparatus according to claim 1; and a lensattached to the driven member.
 6. A lens driving apparatus comprising:the driving apparatus according to claim 2; and a lens attached to thedriven member.
 7. A lens driving apparatus comprising: the drivingapparatus according to claim 3; and a lens attached to the drivenmember.
 8. A lens driving apparatus comprising: the driving apparatusaccording to claim 4; and a lens attached to the driven member.
 9. Animage pickup apparatus comprising the lens driving apparatus accordingto claim 5; an image pickup element that converts an image picked-upthrough the lens into an electrical signal.
 10. An image pickupapparatus comprising the lens driving apparatus according to claim 6; animage pickup element that converts an image picked-up through the lensinto an electrical signal.
 11. An image pickup apparatus comprising thelens driving apparatus according to claim 7; an image pickup elementthat converts an image picked-up through the lens into an electricalsignal.
 12. An image pickup apparatus comprising the lens drivingapparatus according to claim 8; an image pickup element that converts animage picked-up through the lens into an electrical signal.